The present invention relates to room temperature vulcanizable silicone rubber compositions and more particularly the present invention relates to room temperature vulcanizable silicone rubber compositions with a very low modulus.
One component room temperature vulcanizable silicone rubber compositions (hereinafter referred to as RTV compositions) are well known. In particular the most common of such compositions comprise a silanol end-stopped diorganopolysiloxane polymer as the base polymer and methyl triacetoxy silane or methyltrimethoxy silane as the cross-linking agent. To such ingredients there may be further added other ingredients such as extending and reinforcing fillers, flame retardent additives, solvent resistant additives and other additives which are wellknown in the art. The composition is prepared by taking the ingredients and mixing them in such a way as to make them substantially anhydrous by removing most of the moisture from the ingredients. The compositions are then stored as such in caulking tubes or smaller tubes and when it is desired to cure the composition, the seal on the container is broken, the RTV composition is applied in whatever form desired and exposed to atmospheric moisture. Upon exposure to atmospheric moisture the composition cross-links to the silicone elastomer with complete cure taking place in about 24 hours through a thickness of approximately 1/8 in. While acyloxy-functional silane and alkoxy functional silane cross-linking agents are the most well-known of the cross-linking agents in RTV compositions, there are other cross-linking silanes and siloxanes that may be utilized to prepare one part RTV compositions. As to ketoxime functional silane RTV compositions, note the disclosure of Beers, et al. U.S. Pat. No. 3,962,160, which is hereby incorporated by reference. Besides the one-component compositions, there are also well-known two-component compositions. One type of twocomponent RTV composition is generally comprised of silanol end-stopped diorganopolysiloxane as the base polymer which is cross-linked with aminoxy functional silane. In such compositions there is also incorporated fillers and other desirable ingredients. When it is desired to cure the composition, the aminoxy functional silicone compound is added to the silanol base polymer and other ingredients. The composition then cross-links to form a silicone elastomer. The difficulty with such two component RTV compositions is that it requires rather precise metering of the cross-linker into base silanol polymer and, of course, also requires more mixing time and application time which increases the labor cost necessary to use or apply the composition. Disclosures of such aminoxy functional RTV compositions is, for instance, to be found in disclosures of the following patents: Murphy, U.S. Pat. No. 3,528,941; Murphy, U.S. Pat. No. 3,441,583; Murphy, U.S. Pat. No. 3,926,199; Murphy, U.S. Pat. No. 3,341,486. The disclosure of all these patents are incorporated into the present case by reference. There are other aminoxy functional silicone patents which are not disclosed above which relate to other aspects of an aminoxy functional silicone compositions. The above patents are representative of such compositions.
It should be noted that there are also known amide functional RTV compositions, as for instance to be found in the-disclosure of Golitz et al, U.S. Pat. No. 3,417,047 which is hereby incorporated into the present case by reference. This patent disclosed an acetamide or amide functional one-component RTV composition which is formed by mixing a base-silanol end-stopped diorgano-polysiloxane polymer with an amide functional silane or siloxane cross-linking agent where there is at least 3 amide radicals per silicon atom. Such a composition did produce a one-component RTV composition. It has one difficulty and that is it would tend to cure prematurely in the package and thus had a poor shelf life. In addition, when it was applied it would cure very rapidly even in the case where the composition was used soon after it has been packaged. See also compositions as disclosed in Klebe U.S. Pat. No. 3,488,371, which is incorporated into the present case by reference. Accordingly, as noted above while the aminoxy functional silicone compositions and the ketoxime functional compositions were suitable compositions, the difficulty with the aminoxy system was that it was a two component packaged form while the ketoxime system did not appear to give sufficient advantages over the more simple acyloxy functional system so as to warrant such system being widely used.
It should be noted that the amide one-component RTV system also had disadvantages. However, recently there has been evidenced a need for a certain type of one-component RTV system. In concrete road beds, the joint between the concrete blocks in the highway is usually sealed with a tar of some type or other. It has been noted that such tarry substances could not take the contraction and expansion of the concrete road blocks sufficiently and thus after a period of time would crack and permit water to seep underneath the concrete block road bed. The cracking of the tar joint and the allowing of water to get in beneath the concrete blocks and in the joint between the concrete blocks resulted in undesired freezing of the joint and around the joint which resulted in premature cracking of the concrete blocks on the road bed. Accordingly, it was highly desirable to find a different type of sealer for joints between concrete blocks and one that had a sufficiently low modulus such that it would expand and contract sufficiently with the contraction and expansion of the concrete blocks through various extreme temperatures. It was desirable that such joint filler compound not only have a low modulus but also have a certain amount of adhesiveness to concrete substructures with or without a primer. One component RTV compositions and two component systems were suggested for such a use. However, the existing compositions did not appear suitable. Two component RTV systems did not have a high enough modulus and also required sizable labor and specifically skilled labor to apply the compositions as stated previously. With respect to the one-component systems, such one-component systems do not have a low enough modulus or do not have sufficient adhesion to the concrete. It appears that one attempt to produce a one-component RTV system with a sufficiently low modulus cured silicone elastomer was a system disclosed in Klosowski, U.S. Pat. No. 3,996,184 which is incorporated into the present case by reference. Such a composition comprises as a basic ingredient a silanol end-stopped polysiloxane, as a coupler a difunctional amide and specifically methyl vinyl di-(N-organo acetamido) silane and as a cross-linker an aminoxy functional polysiloxane as disclosed in the foregoing Murphy patents. The function of the coupler was that the amide groups would immediately add on to the silanol end-stopped diorganopolysiloxane polymer. Then when the composition was exposed to atmospheric moisture, the minor amount of aminoxy cyclopolysiloxane would crosslink the system to form a silicone elastomer of low modulus. This composition was not desirable since it utilized a solvent. Accordingly, it was highly desirable to find a one-component RTV system with a sufficiently low modulus which would bound to concrete with a primer. Accordingly, it was highly desirable to find a one component RTV system with sufficiently low modulus and with superior adhesion to concrete and other types of masonary substrates.
It is one object of the present invention to provide for a one-component RTV system with an extremely low modulus. It is an additional object of the present invention to provide a one-component RTV system with an extremely low modulus and sufficient adhesion to masonary substrates with as a cross-linker a ketoxime functional silicone compound.
It is another object of the present invention to provide a one-component RTV system with an extremely low modulus with sufficient adhesion to masonary substrates which has as the cross-linker an aminoxy functional silicone compound. It is yet an additional object of the present invention to provide for a process for producing a one-component RTV composition with an extremely low modulus. These and other objects of the present invention are accomplished by means of the disclosures set forth herein below.